Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare destructiveHint=true and idempotentHint=false, and the description adds genuinely new behavior: cancellation is not retroactive ('Emails already delivered are not recalled') and is state-restricted. It stops short of saying what the campaign's resulting status is or how a second call behaves, so it is strong but not exhaustive.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with the action and its valid states, then the exclusion, then the irreversibility caveat. Nothing is redundant with the title or the schema.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a one-parameter destructive tool with full schema coverage and annotations, the description covers eligibility, the alternative, and non-reversibility. The only real gap is the post-call state of the campaign (and there is no output schema to cover it), which is minor but would help an agent confirm success.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% and the single 'id' parameter already documents that it accepts a cmp_xxx ID or a name. The description adds no syntax, resolution, or ambiguity-handling detail beyond the schema, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (cancel) and resource (campaign) plus the eligible states (draft or sending), which immediately separates it from delete-campaign and send-campaign in the sibling list. An agent can pick this tool without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly names the excluded state ('Scheduled campaigns cannot be canceled') and routes the agent to the correct alternative ('delete them to stop the send'). That is a concrete when-not plus a named fallback, not just implied usage.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.